The present invention relates to a new and improved valve assembly which functions as a pressure limiting valve.
A known valve assembly 10 is illustrated in FIG. 1 of the drawings and is utilized in a hydraulic power steering system as a pressure limiting valve. The valve assembly 10 also functions as a reverse flow check valve.
The known valve assembly 10 of FIG. 1 is enclosed in a housing 12 having a main section 14 and a cap 16. The valve assembly 10 is disposed in a valve cavity 20 having an inlet passage 22 and an outlet cavity or passage 24. The valve assembly 10 includes a valve member 28 having a head end portion 30.
A valve seat 32 is pressed against a sealing surface 34 on the housing 12 by a preload spring 36. A primary spring 40 extends around a valve stem 42. The primary spring 40 presses the valve seat 32 against the head end portion 30 of the valve member 28.
An external thread convolution 44 (FIG. 1) on the valve stem 42 is engaged by a spring retainer 46. The spring retainer 46 holds the primary spring 40 and a damping disk 48 on the valve stem 42.
When the known valve assembly 10 is being assembled, an internal thread convolution 52 on the spring retainer 46 is moved into engagement with the external thread convolution 44 on the valve stem 42. The spring retainer 46 is rotated relative to the valve stem 42 to compress the primary spring 40 against the valve seat 32 and head end portion 30 of the valve member 28. When the spring retainer 46 has been moved toward the left (as viewed in FIG. 1) to a desired position relative to the valve stem 42, the spring retainer is fixedly connected to the valve stem by a weld 56.
Valve assemblies having the same general construction as the valve assembly 10 of FIG. 1 have previously been utilized in many different types of hydraulic systems. Difficulty is encountered in manufacturing a quantity of the valve assemblies 10 having the same characteristics. This is because the preload on the primary spring 40 may be different in different valve assemblies.
In addition, when the weld 56 is formed between the spring retainer 46 and valve stem 42, there may be a tendency for the position of the spring retainer 46 to change relative to the head end portion 30 of the valve member 28 with a resulting change in the preload on the primary spring 40. If a valve assembly 10 does not have the desired characteristics, the weld 56 makes it impractical to adjust the valve assembly to have the desired characteristics. This can result in the scrapping of valve assemblies during production with a resulting increase in production costs.